Bollard light mystery IR readings?

[Lew2186]

Hi everyone.

Hopefully someone can help with a little mystery i had today. The issue is fixed but I want to understand what was going on to help in the future.

Fault Finding a tripping fault on some bollard lights. Low IR L - CPC/N - CPC. It was an easy fix, whoever had done it originally had gone the carrier bag and duct tape route to waterproof all the connections. Re did it all, testing as I put it back together, all good.

So the supply cable comes out of the garage, serves a few lights (mains voltage), then dives under a path to a JB where these bollards connect to. Here's where I started scratching my head.

The supply cable was disconnected from the consumer unit.

There were 3 radials coming out of this JB to supply the bollard lights (#1 had 1 light, #2 had 1 light, #3 had 4 lights) and I tested each leg individually. With everything back together and connected to the circuit. I was getting >200 on an IR test. The supply cable going back the other way was around 20 meg ohm, so not perfect but easily good enough.

I connected them all into the JB, went back to the board to test and I was then getting 0.06 between both live conductors and cpc??

After going through it all, not finding anything and wasting an hour chasing a fault that wasnt there, I decided there was nothing wrong with it and hooked it back up. Flipped the switch and everything came on.

The bollards are LED ingrated class 2 units

There's clearly some circuitry in the integrated fittings but why would they test fine individually and only start acting up the second they're all linked together??

Any info would be greatly appreciated

Cheers

 

[timhoward]

With everything back together and connected to the circuit. I was getting >200 on an IR test. The supply cable going back the other way was around 20 meg ohm, so not perfect but easily good enough.

What was connected back at the board at this point?
e.g. maybe L and N were out, but what about CPC, and maybe sheath of SWA?

I connected them all into the JB, went back to the board to test and I was then getting 0.06 between both live conductors and cpc??

Being honest I wouldn't have energised that.
Same question, was everything back together?

Would it make sense that in scenario 1 there was a fault to the SWA armour that wasn't detected, and in scenario 2 it would have been?

 

[Lew2186]

Nothing in the board at all. CPC disconnected

It's honestly very bizarre, never had anything like it.

So testing individual legs from the JB going to the lights IR was fine. Between everything, including SWA armouring. Back to the board also fine. Tested the supply cable from board end while disconnected, also fine.

Connect the 3 radials onto JB, test at board and get 0.06??? No nicks in Insulation in JB or anything either.

I get the whole more cable more leaks regarding IR but the numbers weren't anywhere near concerning. I'm 100% certain there's no fault. I'm just wondering what could possibly cause it other than some kind of electronics in the lights. And even then why would it only show up when they're all connected together.

 

[timhoward]

Is it plastic or metal joint box?
I'm completely guessing but most likely to me is that there's a fault to the armour on the supply cable that got missed when both ends were out. When the gland is back in the joint box, that is connecting CPC and armour by some means (ideally a banjo / earthing nut but might be via a metal box and anywhere on the 3 branches) and the issue can then be measured.

I get the whole more cable more leaks regarding IR but the numbers weren't anywhere near concerning. I'm 100% certain there's no fault.

I'm being brutal but your final IR results are concerning! I realise you were out of ideas but <1Mohm shouldn't be energised.

 

[Lew2186]

Plastic joint box

IR tests were done between live conductors/cpc and the SWA armouring as well, results were fine.
No damage to insulation where glands are made off.

Something else to note which I forgot to mention. The connection of each leg caused the same result. Connect leg 1 on its own to supply cable, 0.06. Leg 2 to supply cable on its own 0.06. Leg 3 on its own... etc. 0.06. And once again, legs on their own & supply cable on its own are all easily passing.

This is when they are all separated and share no common conductors. It has to be something in the lights causing it no? It's the only common denominator in all these tests?

 

[Lew2186]

Tomorrow I'm actually going to go back and disconnect just the fittings. Leave all JBs and everything else in situ. See what I get then. If numbers shoot up then that'll confirm it.

Just for the record the customer is on holiday and I have a key for access. I wouldn't leave something I was unsure on like that.

 

[timhoward]

Any update on this?

This is when they are all separated and share no common conductors. It has to be something in the lights causing it no? It's the only common denominator in all these tests?

It's certainly interesting! (The other common denominator is the supply cable)

Tomorrow I'm actually going to go back and disconnect just the fittings. Leave all JBs and everything else in situ. See what I get then. If numbers shoot up then that'll confirm it.

We are then basically saying that a cable with lights connected measures fine, then simply extending the cable causes 0.06Mohms.

Out of interest, do a L-N test of the 3 cables with lights, at 250v.
Other thought - it sounds obvious but check the same cores are used for N and CPC both ends of the supply cable!

 

[UNG]

So the supply cable comes out of the garage, serves a few lights (mains voltage), then dives under a path to a JB where these bollards connect to. Here's where I started scratching my head.

The supply cable was disconnected from the consumer unit.

There were 3 radials coming out of this JB to supply the bollard lights (#1 had 1 light, #2 had 1 light, #3 had 4 lights) and I tested each leg individually. With everything back together and connected to the circuit. I was getting >200 on an IR test. The supply cable going back the other way was around 20 meg ohm, so not perfect but easily good enough.

So if I'm understanding this correctly the supply cable to the bollard JB has light fittings connected to it before it reaches the bollard JB, if this is the case I would be looking to break the supply cable at each of the light fittings and test each length of cable through to the JB.
If the original installer has used the carrier bag and duct tape on a joint once is there anywhere else they may have buried or hidden a similar joint

After going through it all, not finding anything and wasting an hour chasing a fault that wasnt there, I decided there was nothing wrong with it and hooked it back up. Flipped the switch and everything came on.

Clearly from your testing there is a fault so how did you conclude you were chasing a fault that wasn't there, if there isn't an installation fault then you would have to suspect an issue with your test equipment / leads which would then cast doubt on the readings you have posted

From past experience it is all to easy to assume it's an easy fix and it is some of the apparently easy jobs that take the longest time to fix

 

[SparkySy]

Nothing in the board at all. CPC disconnected

When you did the further testing and got the 0.06 reading were the CPC's back in the consumer unit?
Really when testing you should leave the CPC's in the earth bar just to make sure that the fault in question is not earthing through some other circuit or extraneous conductive part or parallel path.
How did your tests go yesterday?
Sy